Scanner with modular array of photocells

ABSTRACT

A line scanning apparatus employing a multiplicity of linear arrays, the linear extent of which is less than the length of the scan line. To permit an entire line to be covered, the arrays are offset from one another in the direction of scan with adjoining array ends overlapped. To correct for the misalignment and redundancy introduced, the image data from the arrays is buffered until a line is completed when readout, is initiated. During readout, cross over from one array to the next is effected within the overlapped areas and the redundant data discarded.

This invention relates to raster input scanners and, more particularlyto, raster input scanners having multiple linear arrays.

Scanning technology has progressed rapidly in recent years and todayarrays of fairly substantial linear extent are available for use inraster scanners. Indeed, the linear extent of new arrays are in somecases many times the linear extent of earlier array designs. However,the length of even these recent array designs is still not sufficient toenable a single array to span the entire width of the normal sized line,i.e. 81/2 inches. Further, it appears improbable that arrays ofsufficient length will be developed in the foreseeable future sincefabrication of such arrays would appear to require a major breakthroughin semiconductor fabrication technology.

As a result, raster input scanners are forced to rely on shorter arraysand must, therefore, employ a multiplicity of arrays if the entire lineis to be scanned in one pass. This raises the question of how to placethe arrays so as to cover the entire line yet provide datarepresentative of the line which is free of aberrations at the arrayjunctures. Recently, interest has been expressed in optically-buttedarrays. However, optical and optical/mechanical arrangements oftenexperience difficulty in meeting and maintaining the tight tolerancesnecessary for aberration free scanning, particularly in operatingmachine environments.

It is, therefore, a principal object of the present invention to providea new and improved raster input scanner employing multiple arrays.

It is an object of the present invention to provide an improved singlepass line scanner employing multiple linear arrays.

It is an object of the present invention to provide a system designed toaccommodate misalignment of plural linear arrays.

It is an object of the present invention to provide, in a raster inputscanner having multiple physically offset and overlapping linear arrays,means for removing offset and redundancy from the data produced.

It is an object of the present invention to provide scanning apparatuswith plural relatively short linear arrays, having a composite length atleast equal to the scan width.

It is an object of the present invention to provide a line scannerincorporating plural overlapping arrays whose composite length equalsthe length of the scanned lines, with electronic means for switchingfrom one array to the next without introducing noticeable aberrationsand stigmatism.

It is an object of the present invention to provide multiple lineararrays having overlapping viewing fields with data readout bridgingbetween arrays in the overlapping fields thereof.

This invention relates to apparatus for scanning an image line by lineto produce data representative of the image scanned, the improvementcomprising: a movable carriage; at least two arrays, each of the arrayscomprising a plurality of discrete photosensitive elements arranged insuccession along the linear axis of the array, the length of each arraybeing less than the width of the image scanned; means supporting saidarrays on the carriage for scanning the image with the linear axis ofthe arrays extending in a direction substantially perpendicular to thedirection of scanning movement of the carriage, the arrays beingsupported so that the arrays overlap whereby to provide a compositearray having a length at least equal to the width of the image scanned;means for actuating the carriage and the arrays to scan the image; andreadout means for reading out data from the arrays in succession, thereadout means crossing over from one array to the next succeeding arraywithin the array overlap.

Other objects and advantages will be apparent from the followingdescription and drawings in which:

FIG. 1 is an isometric view showing a raster input scanner incorporatingthe multiple array arrangement of the present invention;

FIG. 2 is a schematic illustrating an exemplary array disposition;

FIG. 3 is an schematic view of the scanner operating control;

FIG. 4 is a schematic representation of the memory buffer fortemporarily storing image data;

FIG. 5 is a schematic illustration of the data mapping arrangement toavoid bit shifting on readout from the temporary memory buffer of FIG.4;

FIG. 6 is a schematic view showing the data readout system;

FIG. 7 is a schematic illustration of the data readout with crossoverand removal of redundant data;

FIG. 8 is a schematic view illustrating a modified array wherein thecenter-to-center distances between the photosensitive elements of aportion of one array are changed to provide a vernier useful foraligning arrays;

FIG. 9 is a schematic view of an alternate array configuration wherein abridging array is employed to effect continuity between adjoiningarrays; and

FIG. 10 is a schematic view of another alternative array configurationwherein a bridging array is combined with a standard array to form aunitary structure, the photosensitive elements of the bridging arraybeing on different center-to-center distances to provide a vernier.

Referring to FIG. 1, an exemplary raster input scanning aparatus 10 isthereshown. Scanning apparatus 10, as will appear more fully hereinscans an original document 12 line by line to produce a video signalrepresentative of the original document 12. The video signal so producedmay be thereafter used to reproduce or duplicate the original 12, orstored in memory for later use, or transmitted to a remote source, etc.

Scanning apparatus 10 comprises a box-like frame or housing 14, theupper surface of which includes a transparent platen section 16 on whichthe original document 12 to be scanned is disposed face down. Adisplaceable scanning mechanism designated generally by the numeral 18,is supported on frame 14 below platen 16 for movement back and forthunderneath the platen 16 and the original document 12 thereon in the Ydirection as shown by the solid line arrow in FIG. 1.

Scanning mechanism 18 includes a carriage 20 slidably supported uponparallel rods 21, 22 through journals 23. Rods 21, 22, which parallelthe scanning direction along each side of platen 16, are suitablysupported upon the frame 14.

Reciprocatory movement is imparted to carriage 20 by means of a screwtype drive 24. Drive 24 includes a longitudinally extending threadeddriving rod 25 rotatably journalled on frame 14 below carriage 20.Driving rod 25 is drivingly interconnected with carriage 20 through acooperating internally threaded carriage segment 26. Driving rod 25 isdriven by means of a reversible motor 28.

A plurality of photosensitive linear arrays 1, 2, 3, 4 are carried onplate-like portion 35 of carriage 20. Arrays 1, 2, 3, 4 each comprise aseries of individual photosensitive picture elements or pixels 40arranged in succession along the array longitudinal axis. The arraysscan the original document 12 on platen 14 as scanning mechanism 18moves therepast, scanning movement being in a direction (Y)substantially perpendicular to the array longitudinal axis (X). As bestseen in FIG. 2, the arrays 1, 2, 3, 4 may, due to the difficulty inaccurately aligning the arrays one with the other, be offset from oneanother in the direction of scanning movement (the Y direction). Toaccommodate the relatively short length of the individual arrays, thearrays overlap. In the exemplary illustration, the end portion of arrays2, 1, 4 overlap the leading portion of the succeeding arrays 1, 4, 3when looking from left to right in FIG. 2 along the X direction.

As will be understood, the length of the individual arrays 1, 2, 3, 4may vary with different types of arrays and from manufacturer tomanufacturer. As a result, the number of arrays required to cover theentire width of the original document 12 may vary from that illustratedherein.

Photosensitive elements or pixels 40 of arrays 1, 2, 3, 4 are normallysilicon with carrier detection by means of phototransistors,photodiode-MOS amplifiers, or CCD detection circuits. One suitable arrayis the fairchild CCD 121 - 1728 pixel 2-phase linear array manufacturedby Fairchild Corporation. As described, arrays 1, 2, 3, 4 are offsetfrom one another in the scanning or sagittal direction (Y direction) butwith an end portion of each array overlapping the leading portion of thenext succeeding array to form in effect a composite unbroken array.

To focus the image onto the arrays 1, 2, 3, 4 a lens 43 is provided foreach array. Lenses 43 are supported on carriage 20 in operativedisposition with the array 1, 2, 3, 4 associated therewith. Mirrors 44,45 on carriage 20 transmit the light images of the original via lenses43 to arrays 1, 2, 3, 4. Lamp 48 is provided for illuminating theoriginal document 12, lamp 48 being suitably supported on carriage 20.Reflector 49 focuses the light emitted by lamp 48 onto the surface ofplaten 16 and the original document 12 resting thereon.

In operation, an original document 12 to be scanned is disposed onplaten 16. The scanning mechanism 18 including motor 28 is actuated,motor 28 when energized operating driving mechanism 24 to move carriage20 back and forth below platen 16. Lamp 48 is energized during thescanning cycle to illuminate the original document 12.

To correlate movement of carriage 20 with operation of arrays 1, 2, 3, 4an encoder 60 is provided. Encoder 60 generates timing pulsesproportional to the velocity of scanning mechanism 18 in the Ydirection. Encoder 60 includes a timing bar 61 having a succession ofspaced apertures 62 therethrough disposed along one side of the path ofmovement of carriage 20 in parallel with the direction of movement ofcarriage 20. A suitable signal generator in the form of a photocell-lampcombination 64, 65 is provided on carriage 20 of scanning mechanism 18with timing bar 61 disposed therebetween.

As carriage 20 of scanning mechanism 18 traverses back and forth to scanplaten 16 and any document 12 thereon, photocell-lamp pair 64, 65 ofencoder 60 moves therewith. Movement of the photocell-lamp pair 64, 65past timing bar 61 generates a pulse-like output signal in output lead66 of photocell 64 directly proportional to the velocity of scanningmechanism 18.

As can be envisioned by those skilled in the art, supporting arrays 1,2, 3, 4 in exact linear or tangential alignment (along the X-axis) andmaintaining such alignment throughout the operating life of the scanningapparatus is extremely difficult and somewhat impracticable. To obviatethis difficulty, arrays 1, 2, 3, 4 are initially mounted on carriage 20in substantial tangential alignment. As can be seen in the exemplaryshowing of FIG. 2, this nevertheless often results in tangential arraymisalignment along the x-axis. If the disposition of the arrays 1, 2, 3,4 is compared to a predetermined reference, such as the start of scanline 101 in FIG. 2, it can be seen that each array 1, 2, 3, 4 isdisplaced or offset from line 101 by some offset distance d₁, d₂, d₃,d₄, respectively. As will appear more fully herein, the individualoffset distances of each array 1, 2, 3, 4 is determined and the resultprogrammed in an offset counter 120 (FIG. 3) associated with each array.Offset counters 120 serve, at the start of the scanning cycle, to delayactivation of the array associated therewith until the interval d₁, d₂,d₃, d₄, therefor is taken up.

Referring to FIG. 3, the pulse-like signal output of encoder 60 which isgenerated in response to movement of carriage 20 in the scanningdirection (Y-direction), is inputted to a phase locked frequencymultiplier network 100. Network 100, which is conventional, serves tomultiply the relatively low frequency pulse-like signal input of encoder60 to a high frequency clock signal in output lead 103. Feedback loop104 of network 100 serves to phase lock the frequency of the signal inlead 103 with the frequency of the signal input from encoder 60.

As will be understood, changes in the rate of scan of carriage 20produce a corresponding change in the frequency of the pulse-like signalgenerated by encoder 60. The frequency of the clock signal produced bynetwork 100 undergoes a corresponding change. This results in a highfrequency clock signal in output lead 103 directly related to thescanning velocity of carriage 20, and which accommodates variations inthat velocity.

The clock signal in output lead 103 is inputted to programmablemultiplexer 106. The output of a second or alternate clock signal sourcesuch as crystal controlled clock 108 is inputted via lead 109 tomultiplexer 106. Multiplexer 106 selects either network 100 or clock 108as the clock signal source in response to control instructions (CLOCKSELECT) from a suitable programmer (not shown). The selected clocksignal appears in output lead 111 of multiplexer 106.

An operating circuit 114 is provided for each array 1, 2, 3, 4. Sincethe circuits 114 are the same for each array, the circuit 114 for array1 only is described in detail. It is understood that the number ofcircuits 114 is equal to the number of arrays used.

Operating circuit 114 includes a line transfer counter 115 forcontrolling the array imaging line shutter or sample time for each scan.Counter 115 is driven by the clock signal in output lead 111 ofmultiplexer 106. It is understood that where the signal input to counter115 comprises the clock signal produced by network 100, array samplesize remains constant irrespective of variations in the velocity ofcarriage 20. In other words, where carriage 20 slows down, array shuttertime becomes longer. If carriage 20 speeds up, array shutter timebecomes shorter.

Initial actuation of line transfer counter 115 is controlled by theoffset counter 120 associated therewith. Offset counter 120, which isdriven by the clock signal in output lead 111, is preset to toll a countrepresenting the time interval required for array 1 to reach start ofscan line 101 following start up of carriage 20. On tolling the presetcount, offset counter 120 generates a signal in lead 122 enabling linetransfer counter 115.

It will be understood that the offset counters 115 associated with thecircuits 114 for the remaining arrays 2, 3, 4 are similarly preset to acount representing the distance d₂, d₃, d₄, respectively by which arrays2, 3, 4 are offset from start of scan line 101.

Referring particularly to FIG. 2 each array 1, 2, 3, 4 scans a portionof each line of the original document 12, the sum total of the data(less overlap as will appear more fully herein) produced by arrays 1, 2,3, 4 representing the entire line. Preferably, arrays 1, 2, 3, 4 are ofthe same size with the same number of pixels 40. As described, the linetransfer counters 115 of circuits 114 control the array imaging lineshutter time for each scan, counters 115 being preset to activate thearray associated therewith for a preselected period for this purpose.Scanned data from the arrays 1, 2, 3, 4 is clocked out by clock signalsderived from a suitable pixel clock 118.

Sampled analog video data from the arrays 1, 2, 3, 4 is fed to asuitable video processor 148 which converts the video signals to abinary code representative of pixel image intensity. The binary pixeldata from processor 148 is mapped into segments or words by Pixel DataBit Mapper 149 for storage in offset relation in RAM 175 as will appear.Bit Mapper 149 is driven by clock signals from pixel clock 118. Datafrom Bit Mapper 149 is passed via data bus 174 to RAM 175 where the datais temporarily stored pending receipt of data from the array which lastviews the line. In the exemplary arrangement illustrated, the last arraywould be array 4.

Multiplexer 150 may be provided in data bus 174 to permit data fromother sources (OTHER DATA) to be inputted to RAM 175.

The binary data is stored in sequential addresses in RAM 175 (see FIG.4), the data being addressed into RAM 175 on a line by line basis by theRAM address pointers 165 through Address Bus 180. The clock signaloutput from pixel clock 118 is used to drive address pointers 165. Linescan counter 170, which is driven by the output from line transfercounter 115, controls the number of full scan lines that will be storedin RAM 175 before recycling. The output of counter 170 is fed to RAMAddress pointer 165 via lead 119. It is understood that line scancounters 170 are individually preset to reflect the degree of arrayoffset in the Y-direction.

Ram 175 provides a buffer for scanned data from each array, RAM 175buffering the data until a full line is completed following which thedata is read out. A suitable priority encoding system (not shown) may beused to multiplex the data input from arrays 1, 2, 3, 4 with the addressassociated therewith. Ram 175 has input and output ports for input andoutput of data thereto.

Since the degree of misalignment of arrays 1, 2, 3, 4 in the Y-directionmay vary, the storage capacity of RAM 175 must be sufficient toaccommodate the maximum misalignment anticipated. A worst casemisalignment is illustrated in FIG. 4 wherein it is presumed that arrays1, 2, 3, 4 are each misaligned by a full line. In that circumstance andpresuming scanning of line l is completed, RAM 175 then stores the linedata for lines l, l₁, l₂, l₃, l₄ from array 1, lines l, l₁, l₂, l₃ fromarray 2, lines l, l₁, l₂ from array 3, and lines l, l₁ from array 4. Theblocks of binary data that comprise the completed line 1 are incondition to be read out of RAM 175. In the above example, an extra lineof data storage is provided.

Line scan counters 170 are recycling counters which are individuallypreset for the number of lines of data to be stored for the arrayassociated therewith. As a result, address pointers 165 operate in roundrobin fashion on a line by line basis. On reaching a preset count, thesignal from counters 170 recycle the address pointer 165 associatedtherewith back to the first storage line to repeat the process. It isunderstood that prior thereto, that portion of RAM 175 has been clearedof data.

As described, data from video processing hardware 148 is storedtemporarily in RAM 175 pending completion of the line. In placing thedata in RAM 175, the data is preferably mapped in such a way as to avoidthe need for subsequent data bit shifting when outputting the data.Referring to FIG. 5, wherein mapping of pixel data from arrays 1, 2 isillustrated, data from an earlier array (i.e. array 1) is mapped byPixel Data Bit Mapper 149 (FIG. 3) into segments or words 180 beforebeing stored in RAM 175. The first pixel (P₁ -1) of the array within thearray overlap 181 is mapped into a known bit position within the segmentor word 180 at the point of overlap.

At the end of line transfer, the first pixel (P₁ -2) of the succeedingarray (i.e. array 2) is clocked into the bit position (P₁ -1) of thefirst overlapped pixel of the previous array. This correlates the firstoverlapping pixel (P₁ -2) of the succeeding array (i.e. array 2) withthe first overlapped pixel (P₁ -1) of the preceding array (i.e. array1). Crossover from one array to the succeeding array on data readout maythen be effected without the need to shift bits.

Referring now to FIGS. 6 and 7, video data held in RAM 175 is read outto a user (not shown) via RAM output bus 176, in both tangentially andspatially corrected form, line by line, through output channel 200. Datareadout is controlled by a microprocessor, herein CPU 204 in accordancewith address program instructions in memory 206. CPU 204 may compriseany suitable commercially available processor such as a Model M6800manufactured by Motorola, Inc.

The address program instructions in memory 206 include a descriptor list207. List 207 contains information identifying the number of bits to beread out (N_(n)), the address of the first word (A), and other userinformation (U). The DATA OUT address information is fed to addressmultiplexer 208 via address bus 209.

As described heretofore, exact tangential alignment and end to endabutment of multiple arrays is difficult to achieve. In the arrangementshown, sagittal misalignment (in the Y direction) among the arrays isaccommodated by offset counters 120 of the individual array operatingcircuits 114. The need to accurately abut the arrays end to end isobviated by overlapping succeeding arrays.

As a result of the above, the sequence in which video data is inputtedto RAM 175 offsets sagittal misalignments between the several arrays. Byoutputting the data from RAM 175 on a line by line basis, the lines arereconstructed without sagittal misalignment.

Due to the overlapping disposition of arrays 1, 2, 3, 4, data within theoverlapping portions of the arrays is redundant. To obviate this andprovide a complete line of data without repeated or redundant portions,bit crossover on readout within the overlapping regions is used.

Referring now to the embodiment shown in FIG. 7, data bit crossoverwithin the overlapping portions of arrays 1, 2, 3, 4 is effected by analgorithm which picks a predetermined last cell to be sampled within theoverlapped region and automatically picks the next bit in the succeedingarray. In the descriptor list 207 illustrated in FIG. 7, the total bitoutput from the first array is N₁ bytes + n₁ bits with the bit outputfrom the second array N₂ bytes - n₂ bits. In the example shown in FIG.7, crossover from array 2 to array 1 is effected between bit 4 and bit5.

In the arrangement described heretofore, the center-to-center distancebetween successive photosensitive elements or pixels 40 is constant.Referring to FIG. 8, wherein like numerals refer to the like parts apair of arrays 300, 301 are there shown with the end portionsoverlapped. The photosensitive elements or pixels 40 that comprisearrays 300, 301, except for the end 308 of array 300, are on normalcenter-to-center distances d. The photosensitive elements 40' in the end308 of array 300 are set on a slightly reduced center-to-center distanced'. The reduction in center-to-center distances between thephotosensitive elements 40' in end 308 of array 300 provide in effect avernier scale which normally provides at least one point where opposingarrays are in alignment irrespective of the degree of overlap betweenthe arrays. In the exemplary arrangement shown, the end ofphotosensitive element 40 - 8 of array 301 is in substantial alignmentwith the start of photosensitive element 40' - 5 of array 300, andcrossover would be set at this point.

It will be understood that visual identification of the individualphotosensitive elements or pixels 40, 40' to determine the optimumcrossover point may be made through microscopic examination of thearrays. It is further understood that once the optimum crossover pointis determined, the descriptor list of memory 206 (FIGS. 6, 7) isprogrammed to provide crossover from pixels 40 - 8 of array 301 to pixel40' - 5 of array 300 on readout.

While the vernier scale is illustrated as being at one end 308 of array300 only, it is understood that vernier scales may be provided at bothends of the array. In that event, in a scanning arrangement employingfour arrays such as shown in FIG. 2, array 1 may have a vernier scale ofthe type described at each end, array 3 a vernier scale at one end only,with remaining arrays 2, 4 conventional.

While the vernier scale described is established by reducingcenter-to-center distances between adjoining pixels, it is understoodthat a vernier scale may be created by increasing slightly thecenter-to-center distances between adjoining array pixels.

Referring to the embodiment shown in FIG. 9, there a pair of relativelylong linear arrays 350, 351 are disposed end to end. This may beeffected optically as by means of lenses 43 in the scanning apparatus 10of FIG. 1 or mechanically through physical contact of the array endswith one another. To accommodate any gaps between the array ends ormisalignments along the X axis and to assure continuity of the compositearray so formed, a relatively short bridging array 360 is provided tooverlap the adjoining ends of each array 350, 351.

Bridging array 360 comprises a relatively short linear array, preferablywith the minimum quantity of pixels 40 needed to provide effectiveoverlap of the adjoining arrays. Typically, bridging array 360 may becomprised of the order of 100 pixels whereas arrays 350, 351 comprisesome 1700 pixels.

In use, data from arrays 350, 351, 360 may be readout as describedearlier, the data being stored temporarily in RAM 175 (FIG. 3) pendingcompletion of the line. By choosing relatively short bridging arrays360, the amount of data to be stored in RAM 175 and hence the size ofRAM 175 may be substantially reduced. The data held in RAM 175 is, oncompletion of the line, read out from RAM 175 into bus 176 (FIG. 6),with crossover made from array 350 to bridging array 360 and thereafterfrom bridging array 360 to array 351 in the overlapping areas to assurecontinuity.

Referring to the embodiment shown in FIG. 10, where like numerals referto like parts, an array structure 400 is thereshown. Array structure 400includes relatively long and short arrays 402, 404 respectively mountedupon a common substrate or mask 406. Array 404 is disposed in parallelwith array 402, with a portion 409 of array 404 overlapping one end 403of array 402. The remainder of array 404 projects beyond end 403 ofarray 402 and is adapted to overlay the leading end of the nextsuccessive array structure 400' as seen in drawing FIG. 10. Toaccommodate overlapping of successive array structures 400, substrate406 is inset at 407.

To enhance alignment between the arrays and provide undistortedcrossover between arrays, photosensitive elements or pixels 40' of array404 are disposed on a center-to-center distance d' different from thecenter-to-center distance d of pixels 40 of array 402. This in effectestablishes a vernier scale which enables at least one pixel 40' ofarray 404 to be aligned with a corresponding pixel 40 of array 402. Inthe exemplary arrangement shown, pixel 40 - 5 of array 402 is insubstantial alignment with pixel 40' - 4 of array 404 and crossoverwould be effected at this point.

Similarly, when associating the array structure 400 with the nextsucceeding array structure 400', crossover from array 404 to array 402'is selected at the point of closest pixel alignment. In the embodimentshown, crossover would be between pixel 40' - 7 of array 404 and pixel40 - 3 of array 402.

While the center-to-center distance d' between pixels 40' of array 404is illustrated as being less than the center-to-center distance dbetween the pixels 40 of array 402, it is understood that dimension d'may be greater than dimension.

While the invention has been described with reference to the structuredisclosed, it is not confined to the details set forth, but is intendedto cover such modifications or changes as may come within the scope ofthe following claims.

What is claimed is:
 1. An array for use with scanning apparatus of thetype having a plurality of overlapping arrays of photosensitive elementswhich cooperate to form a composite array of substantial length, thecombination of:a. an array support, b. means forming a first lineararray on said support; and c. means forming a second linear array onsaid support, said second linear array being substantially parallel withsaid first array with the linear extent of said first array beinggreater than the linear extent of said second array, said second lineararray having a portion thereof overlaying one end of said first arraywith the remainder of said second linear array projecting beyond saidfirst array one end.
 2. The array according to claim 1 in which thecenter-to-center distance between photosensitive elements of said secondarray is different from the center-to-center distance betweenphotosensitive elements of said first array whereby to facilitatecrossover alignment of at least one photosensitive element in saidsecond array with a photosensitive element in said first array.
 3. Thearray according to claim 2 in which the center-to-center distancebetween photosensitive elements of said second array is less than thecenter-to-center distance between the photosensitive elements of saidfirst array.
 4. The array according to claim 2 in which thecenter-to-center distance between photosensitive elements of said secondarray is greater than the center-to-center distance between thephotosensitive elements of said first array.